But climate sceptics have focused their attention on the references to a pause or hiatus in the increase in global temperatures since 1998.

The sceptics believe that this slowdown is the most solid evidence yet that mainstream computer simulations of the Earth's climate - climate models - are wrong.

These computer simulations are used to study the dynamics of the Earth's climate and make projections about future temperature change.

"The sceptics now have a feeling of being on the winning side of the debate thanks to the pause," said Marcel Crok, a Dutch author who accepts the idea that human activities warm the planet, but is sceptical about the scale of the effect.

Who are the climate sceptics?

Although there are only a small number of mainstream scientists who reject the established view on global warming, they are supported by a larger group of well resourced bloggers and citizen scientists who pore through climate literature and data looking for evidence of flaws in the hypothesis.

There are many different shades of opinion in the sceptical orbit. Some such as the group Principia Scientific reject the "myth" of greenhouse gas warming.

There are also political sceptics, such as some members of the Republican party in the US, who argue that climate science is a hoax or a conspiracy.

But there are also sceptical bloggers such as Anthony Watts and Andrew Montford who accept the basic science that adding carbon to the atmosphere can affect the temperature. They contest mainstream findings on the sensitivity of the climate to carbon and the future impacts on temperature.

"You are now starting to see a normalisation of climate science. Suddenly mainstream researchers, who all agree that greenhouse gases play a huge role, start to disagree about the cause of the pause.

"For me this is a relief, it is finally opening up again and this is good."

The view that the sceptics have positively impacted the IPCC is supported by Prof Arthur Petersen, who is a member of the Dutch government team currently examining the report.

"The sceptics are good for the IPCC and the whole process is really flourishing because of this interaction over the past decades," he told BBC News.

"Our best climate researchers are typically very close to really solid, sceptical scientists. In this sense scepticism is not necessarily a negative term."

Others disagree.

Bart Verheggen is an atmospheric scientist and blogger who supports the mainstream view of global warming. He said that sceptics have discouraged an open scientific debate.

Image caption
Dutch writer Marcel Crok is sceptical about the sensitivity of the atmosphere to carbon emissions

"When scientists start to notice that their science is being distorted in public by these people who say they are the champions of the scientific method, that could make mainstream researchers more defensive.

"Scientists probably think twice now about writing things down. They probably think twice about how this could be twisted by contrarians."

Sensitive debate

In 2007, the IPCC defined the range for what's termed "equilibrium climate sensitivity". This term refers to the likely span of temperatures that would occur following a doubling of CO2 concentrations in the atmosphere.

The panel's last report said temperatures were likely to rise within the range of 2C to 4.5C with a best estimate of 3C.

The new report is believed to indicate a range of 1.5C to 4.5C with no best estimate indicated.

The Dutch approach to sceptics

With around 20% of the country under sea level, the Dutch have a keen interest in anything that might affect their environment, such as climate change.

But scepticism about the human influence on global warming has been growing in the Netherlands, according to research from the OECD.

In a country where consensus is a key word, the government has taken a more inclusive approach to climate dissenters. To that end, they have funded Marcel Crok to carry out a sceptical analysis of the IPCC report.

In an effort to build bridges between sceptics and the mainstream they are also funding an initiative called climatedialogue.org which serves as a platform for debate on the science of global warming.

Although that might not appear like much of a change, many sceptics believe it exposes a critical flaw.

"In the last year, we have seen several studies showing that climate sensitivity is actually much less than we thought for the last 30 years," said Marcel Crok.

"And these studies indicate that our real climate shows a sensitivity of between 1.5C and 2C, but the climate models on which these future doom scenarios are based warm up three degrees under a doubling of CO2."

But other researchers who are familiar with the text believe that the sceptics are reading too much into a single figure.

"Some of what the sceptics are saying is either wishful thinking or totally dishonest," Prof van Ypersele, who is vice-chair of the IPCC, told BBC News.

"It is just a change in a lower border [of the range of temperature rise]. Even if this turns out to be the real sensitivity, instead of making the challenge extremely, extremely, extremely difficult to meet, it is only making it extremely, extremely difficult.

"Is that such a big change?"

Prof van Ypersele points out that many other aspects of the forthcoming report are likely to give greater certainty to the scale of impacts of a warming world. The predictions for sea level rise are likely to be considerably strengthened from 2007. There is also likely to be a clearer understanding of the state of sea ice.